1. Field of the Invention
This invention relates to transversal filter systems and particularly to a one-sided charge coupled transversal filter that operates with a substantially high signal-to-noise ratio.
2. Description of the Prior Art
As is well known in the art, charge coupled device transversal filters provide signal filtering of analog signals using time sampling techniques common to CCD technology. The conventional charge coupled device transversal filter is a two-sided arrangement in which the electrodes are split into an upper and lower portion in a configuration to provide the weighting coefficients with the signals from the upper and lower electrodes being applied to a differential amplifier for developing the transversal filter output. The input signal to be filtered is sampled at at least a rate greater than twice the highest frequency of interest in the signal. This sampling stage is then followed by N delay stages each of which delays a signal sample for one clock period. At each delay stage a signal is nondestructively sampled, multiplied by a predetermined weighting coefficient as a result of the difference in the electrodes widths and the weighted samples are summed to give the filter output V.sub.0. Thus, by splitting alternate buried metal CCD electrodes so that the difference in length of each electrode represents the corresponding weighting coefficient and sensing the displacement current sums in the upper and lower portions, the desired impulse response is provided by the filter. In the conventional two-sided transversal filter noise is generated within the CCD channel, at the reset gate and in the output devices. Noise being generally a limiting parameter in electronic and electro optical systems, a relatively low signal-to-noise ratio substantially degrades overall system performance. Because the capacitance is proportional to electrode area, the conventional two-sided transversal filter has its limitations because of the noise sources in the filter system. It would be of substantial advantage to the art, if a CCD transversal filter were provided that would develop a minimum of noise and that would provide a substantially high output voltage swing.